Many variable displacement engines employ a valve deactivation assembly including a rolling finger follower that is switchable from an activated mode to a deactivated mode. One method for activating and deactivating the rocking arm (e.g., a roller finger follower) includes an oil-pressure actuated latch pin within the inner arm of the rocker arm which, in the activated mode, engages the inner arm and outer arm in a latched condition to actuate motion of the outer arm, thereby moving a poppet valve that controls one of the intake or exhaust of gases in the combustion chamber. In the deactivated mode, the inner arm is disengaged from the outer arm in an unlatched condition, and the motion of the inner arm is not translated to the poppet valve, resulting in a lost motion.
As is typical in the valve deactivator art, mode transitions, either from the latched condition to the unlatched condition, or vice versa, occur only when the cam is on the base circle portion. That is to say, mode transitions are controlled to occur only when the roller follower is engaging the base circle portion of the cam. This is done to ensure that the mode change is occurring while the valve deactivator assembly, and more specifically the latching mechanism, is not under a load. Due to the high rotational speed of a cam, it is desirable, but difficult, to reduce the amount of time needed to transition from a latched condition to an unlatched condition in order to execute the transition during a single base circle period. The inventors have recognized that one problematic issue that may arise during mode transitions in a rolling finger follower with an oil-pressure actuated latch pin is the presence of air trapped within the latch pin circuit, which is compressible and increases the amount of time needed to switch from the latched condition to the unlatched condition or vice versa.
The latch pin hydraulic circuit of a switching rolling finger follower may be primed with a low amount of hydraulic pressure while operating in the latched condition to facilitate the transition to the unlatched condition. In one example, this priming is achieved by utilizing a dual-function hydraulic lash adjuster (HLA) which is configured to provide hydraulic fluid to a latch pin hydraulic circuit at one of a first, lower pressure or a second, higher pressure. The first and second pressures are present at the upper feed port of the hydraulic lash adjuster based on a state of an oil control valve. The hydraulic lash adjuster directs the hydraulic fluid to the latch pin hydraulic circuit via a single port located in a plunger of the lash adjuster. One example approach is shown by Hendriksma et al. in E.P. 1892387. Therein, a dual feed hydraulic lash adjuster is equipped to supply oil to two adjacent oil galleries for valve actuation mechanisms of a cylinder. The two oil galleries are fluidly coupled within the hydraulic lash adjuster in order to provide varying hydraulic fluid pressures to the valve actuating mechanisms dependent on engine conditions. A first gallery flows higher pressure hydraulic fluid to the second gallery in order to carry trapped air in the second oil gallery to a pressure relief valve.
However, the inventors herein have recognized potential issues with such systems. As one example, manufacturing a hydraulic lash adjuster with an internal passage fluidly coupled to both a first gallery and second gallery is difficult and increases a cost and complexity of the hydraulic lash adjuster. As a second example, the first gallery and second gallery are placed at equal heights and on opposite sides of the hydraulic lash adjuster which limits functionality and modularity of the hydraulic lash adjuster, specifically with a variety of variable displacement engines and oil circuit designs. The equal height of the first and second gallery also lead to the need for orientation features on the hydraulic lash adjuster and cylinder head to ensure the proper features are aligned with the respective oil galleries.
In one example, the issues described above may be addressed by a method for closing a control valve to flow hydraulic fluid from a first annular gallery to a second annular gallery of a hydraulic lash adjuster via a metered hydraulic fluid passage positioned between the first and second annular galleries and on an outer surface of a hydraulic lash adjuster body and opening the control valve to flow hydraulic fluid directly to the second gallery from the control valve. In this way, the first and second gallery may be positioned at different heights on any side of the hydraulic lash adjuster and independent of the orientation of the lash adjuster.
As one example, during vehicle operation at higher loads, the control valve may be closed such that all of a hydraulic fluid flows to the first gallery and the second gallery receives lower pressure hydraulic fluid from the first gallery via a metered passage on an outer surface of the hydraulic lash adjuster in order to displace air from the second gallery while maintaining oil pressure sufficiently low to keep a pin of an auxiliary valve actuation system (e.g., a roller finger follower) latched. In this way, all cylinders of an engine are firing and no cylinders may be deactivated. During vehicle operation at lower loads, the control valve may be opened to flow higher pressure hydraulic fluid directly to the second oil gallery via bypassing at least a portion of hydraulic fluid away from the first oil gallery. The high pressure hydraulic fluid flows from the second gallery to the auxiliary valve actuation system to unlatch the pin. In this way, one or more cylinders of an engine may be deactivated while a remaining number of cylinders may be nominally operated based on current engine operating conditions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.